Connect 4 objects with rigid body constraint?
I have a similar setup with multiple hinges. and I got it all to work properly except there is A LOT of play at the actual pivot points. Like rubber or something. The faster the object moves the more play there is in the joint. 

This seems to be a real problem because I have used the exact setup in blender and unity with the same results. I can't find anything anywhere online about this rubbery pivots problem. I've tried making the mass of the objects 0. It had little effect, but it did help. The only thing I can think of is you can't have multiple pivots working on each other.

The way I did it was following this tut.

step by step description on how to connect two objects with a hinge constraint

Again, I think, hinge joints are useless in this case. Sure would be nice if the joints were actually rigid.